The present invention relates to dental drills, particularly to improved dental drills having vicinity imaging capability and, more particularly, to dental drills provided with optical fibers connected to an optical coherence domain reflectometry (OCDR) to image several millimeters ahead of the ablation surface.
In dentistry, drills are used to remove cavities and to prepare for restoration and implants. In many cases it would be valuable to image below the surface being drilled to minimize damage to vital normal tissue. Identifying the boundary between decayed and normal enamel (or dentine) would reduce the removal of viable tissue; and identifying the nerve before getting too close with the drill could prevent nerve damage. Thus, there is a need for dental treatment imaging, and such has been accomplished by the present invention using (OCDR).
Optical coherence domain reflectometry is a technique developed by Youngquist et al. in 1987 (Youngquist, R. C. et al., xe2x80x9cOptical Coherence-Domain Reflectometry: A New Optical Evaluation Technique,xe2x80x9d 1987, Optics Letters 12(3): 158-160). Danielson et al. (Danielson, B. L. et al., xe2x80x9cGuided-Wave Reflectometry with Micrometer Resolution,xe2x80x9d 1987, Applied Physics 26(14): 2836-2842) also describe an optical reflectometer which uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection. OCDR was first applied to the diagnosis of biological tissue by Clivaz et al. in January 1992 (Clivaz, X. et al., xe2x80x9cHigh-Resolution Reflectometry in Biological Tissues,xe2x80x9d 1992, Optics Letters 17(1): 4-6). A similar technique, optical coherence tomography (OCT) has been developed and used for imaging with catheters by Swanson et al. in 1994 (Swanson, E. A. et al., U.S. Pat. Nos. 5,321,501 and 5,459,570. Tearney et al. (Tearney, G. J. et al., xe2x80x9cScanning Single-Mode Fiber Optic Catheter-Endoscope for Optical Coherence Tomograph,xe2x80x9d 1996, Optics Letters 21(7): 543-545) also describe an OCT system in which a beam is scanned in a circumferential pattern to produce an image of internal organs. U.S. Pat. No. 5,570,182 to Nathel et al. describes method and apparatus for detection of dental caries and periodontal disease using OCT. However, as OCT systems rely on mechanical scanning arms, miniaturizing them enough to operate on a guidewire would be very difficult.
Polarization effects in an OCDR system for birefringence characterization have been described by Hee et al. (Hee, M. R. et al., xe2x80x9cPolarization-sensitive low-coherence reflectometer for birefringence characterization and ranging,xe2x80x9d J. Opt. Soc. Am. B, Vol. 9, No. 6, June 1992, 903-908, and in an OCT system by Everett et al. (Everett, M. J. et al., xe2x80x9cBirefringence characterization of biological tissue by use of optical coherence tomography,xe2x80x9d Optics Letters, Vol. 23, No. 3, Feb. 1, 1998, 228-230).
In a prior art OCDR scanning system 10, shown in FIG. 1, light from a low coherence source 12 is input into a 2xc3x972 fiber optic coupler 14, where the light is split and directed into sample arm 16 and reference arm 18. An optical fiber 20 is connected to the sample arm 16 and extends into a device 22, which scans an object 24. Reference arm 18 provides a variable optical delay. Light input into reference arm 18 is reflected back by reference mirror 26. A piezoelectric modulator 28 may be included in reference arm 18 with a fixed mirror 26, or modulator 28 may be eliminated by scanning mirror 26 in the Z-direction. The reflected reference beam from reference arm 18 and a reflected sample beam from sample arm 16 pass back through coupler 14 to detector 30 (including processing electronics), which processes the signals by techniques that are well known in the art to produce back-scatter profile (or xe2x80x9cimagexe2x80x9d) on display 32.
The present invention utilizes a drill surrounded with several optical fibers used by an OCDR to image several millimeters ahead of the ablation surface. The OCDR system translates this information into a profile image of the tissue optical properties near the ablation surface. This information can be displayed to the user, or analyzed by software to sound an alarm, or stop the drill when a selected boundary or distance to sensitive tissue, nerve, blood vessel, etc., is reached.
It is an object of the present invention to enable improved dental drilling procedures.
A further object of the invention is to provide imaging of areas slightly ahead of the ablation area of dental drilling.
A further object of the invention is to provide a method for obtaining images of areas ahead of the ablation area.
It is a further object of the invention to utilize OCDR in combination with a dental drill to enable imaging of areas adjacent the drilling operation.
Another object of the invention is to provide a dental drill with optical fibers connected to an OCDR to enable imaging of areas ahead of the drilling or ablation area.
Another object of the invention is to provide an improved dental drilling system, which includes imaging by the user of the area to be drilled, and to provide an alarm or to stop the drill when a selected boundary or distance from the drilling operation is reached.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. Basically, the invention involves an optical coherence tomography (OCT) guided dental drill. The invention is a dental drill that has one or multiple single-mode fibers that can be used to image in the vicinity of the drill tip. Identifying the boundary between decayed and normal enamel (or dentine) reduces the removal of viable tissue, and identifying the nerve before getting too close with the drill prevents nerve damage. The drill is surrounded with 1, 2,4 or more single-mode optical fibers, which independently couple light from a sample arm of an OCDR system to the tissue to be removed. Light from these OCDR fibers exit the tip and are directed into the hard or soft tissue via small diameter optics (such as gradient index lenses and prisms). The light reflected or scattered from the tissue is then collected by the same optical fibers and detected by the OCDR system, which translates this information into a profile image of the tissue optical properties near the ablation surface. This information can be displayed to the user or analyzed by software to sound an alarm or stop the drill when a selected boundary or distance to sensitive tissue is reached. The invention can use single or multiple OCDR systems (one for each imaging fiber), or can be used with a form of multiplexing.